The present invention relates to an apparatus for modeling a skeletal structure before and after a surgical procedure is performed on the structure. More particularly, it relates to a tool that may be used to model the structure and mechanics of a skeletal joint both before and after an osteotomy is performed on a bone of the joint.
Many medical conditions involving the skeletal system may be remedied by the performance of an osteotomy technique, or the surgical division or sectioning of bone. As an example, a veterinary surgeon may perform a technique known as a tibial plateau leveling osteotomy to remedy problems caused by a weakened or ruptured cranial cruciate ligament in the leg of a dog. When the cranial cruciate ligament of a dog is damaged, the tibia may move forward relative to the femur when the leg is loaded. This forward motion, known as tibial thrust, may cause more severe injury to the dog's leg in the form of soft tissue (medial meniscus) impingement. The forward motion can occur because the tibial plateau, or the region of the proximal end of the tibia that contacts the femur, meets the femur at a non-perpendicular angle relative to the direction of the force the tibia exerts against the femur when the leg is loaded. The tibial plateau leveling osteotomy procedure is used to change the angle at which the tibial plateau contacts the femur to be more perpendicular to the direction of this force. In the procedure, a curvilinear cut is made in the proximal region of the tibia to free a portion of the tibia, including the tibial plateau region, from the rest of the bone. This portion may then be rotated along the curvilinear cut to change the angle at which the tibial plateau meets the femur. After the angle is changed to the desired angle, the bone portion is fixed to the rest of the tibia by conventional means.
Before performing an osteotomy procedure, a physician or veterinarian generally must explain the various aspects of the procedure to the patient or pet owner. For example, the doctor must explain the mechanics of the injured joint, and why the osteotomy is necessary to change the joint structure to fix the joint. The doctor must also explain how the osteotomy is performed, and why the joint will perform better after the surgery. Several methods may be used to convey this information to the patient. First, the doctor may simply talk to the patient. However, many people lack the physiological knowledge or training necessary to understand a discussion of bone mechanics and surgeries, even if the doctor describes the procedure in lay terms. Furthermore, a doctor often needs to use a relatively large quantity of unwieldy language to explain even simple procedures. Thus, a doctor who verbally describes a procedure runs the risk that a patient or pet owner will not understand all aspects of the procedure.
A doctor may also use some sort of visual aid to show the patient or pet owner how the procedure is to be performed. For example, a doctor may make or use two-dimensional illustrations of the joint before and after the surgery is performed to illustrate the procedure. Verbal descriptions combined with illustrations are superior to verbal descriptions alone for several reasons. First, a doctor may convey with a single illustration a complex idea that may be difficult to describe verbally. Also, the doctor may point to the illustration while describing a particular aspect of the joint or surgery to show the patient exactly what is being discussed. If the doctor wants to describe changes in the structure or performance of the joint caused by the surgery, the doctor may use separate illustrations to show the joint structure and mechanics before and after each step in the surgery. Though this method may make the description of the surgery somewhat easier for the patient to understand, it still presents difficulties. Most significantly, it is difficult to represent movement with illustrations. Separate illustrations may show the position of a bone before and after a movement, but the illustrations themselves do not represent the actual movement of the bone between the two positions. Thus, even with the use of two-dimensional illustrations, it remains difficult to explain in a simple manner exactly how the changes in bone structure alter the joint mechanics.
Rather than using two-dimensional illustrations to explain a surgical procedure, a doctor may also use a lifelike, three-dimensional skeletal model as a visual aid. Such models allow the motion of the joint to be demonstrated. However, due to the complexity of bone shapes and joint structures, a lay person may not be able to see subtle features in skeletal structure in these models. As an example, a lay person may have difficulty perceiving the angle at which the tibia meets the femur in a canine knee joint if shown a three-dimensional skeletal model of the joint. Also, these models may be fragile and difficult to transport. Thus, it would be desirable to have a simple apparatus or tool for illustrating the movement of a bone fragment during an osteotomy procedure, and for modeling the mechanics of a joint involved in the procedure both before and after the procedure.